MODIFICATION OF THE ZEOLITE COMPONENT OF A VACUUM GAS OIL HYDROCRACKING CATALYST

A study has been made of the influence of the conditions of modificati on of an ultrastable Y zeolite produced by a method including treatmen t of the zeolite with a solution of ammonium hexafluorosilicate on the physicochemical and catalytic properties of the zeolite. IR spectrosc opy and temperature-programmed desorption of ammonia have been used to study the effect of acid and alkali treatment of an ultrastable Y zeo lite on its crystal structure and acidic properties (overall acidity, the strength distribution of acid centres). The catalytic activity of modified zeolites was assessed from the yield of fuel fractions (gasol ine and diesel) during the hydrocracking of vacuum gas oh. It has been shown that the method of zeolite modification makes it possible to co ntrol its acidic properties as required. The yield of fuel fractions i s determined both by the nature of the acid centres and the ratio of m edium-strength and strong centres and by the process conditions. Depen ding on the demand for preferential production of a particular fuel fr action, the process must be carried out under optimum conditions and o n a catalyst with which the ratio between medium-strength and strong a cid centres is optimum. (C) 1998 Elsevier Science Ltd. All rights rese rved.